The present invention relates generally to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device which can prevent a high resistance compound from being produced due to diffusion of different metals when joining the different metals with each other and a method for forming the same.
In a semiconductor device, metal lines are formed to electrically connect elements or lines with each other. Contact plugs are formed to connect lower metal lines and upper metal lines with each other. As the integration level of the semiconductor continues to increase, the aspect ratio of a contact hole, in which a contact plug is formed, gradually increases. As a result, the difficulty and the importance of a process for forming the metal line and the contact plug have been noted.
The metal line of a semiconductor device is usually formed of aluminum or tungsten because both have good electrical conductivity. Recently, research has been conducted regarding the use of copper to form the metal line of a semiconductor device because copper has excellent electrical conductivity and copper has a low resistance when compared to aluminum and tungsten. Forming the metal line of a semiconductor device with copper (Cu) can therefore solve the problems associated with conventional metal lines of highly integrated semiconductor devices having high operating speed such as RC signal delay.
It is difficult to dry-etch copper into a wiring pattern, and therefore to form a metal line using copper a damascene process is employed.
In the damascene process, a metal line forming region is formed by etching an interlayer dielectric, and a metal line is formed by filling a metal layer (i.e., a copper layer) in the metal line forming region. Here, the metal line forming region can be formed through one of a single damascene process and a dual damascene process. In particular, in the dual damascene process, an upper metal line and a contact plug for connecting the upper metal line and a lower metal line can be simultaneously formed. Also, since surface undulations that are produced due to the presence of the metal line can be removed, a subsequent process can be conveniently conducted.
When forming a multi-layered metal line using the damascene process, copper may be used as the material for a lower metal line and aluminum is used as the material for an upper metal line, when different metals are joined with each other as described above, a high resistance compound may be produced due to diffusion of the respective metals. Therefore, in order to prevent the high resistance compound from being produced, a diffusion barrier must be formed on the interface of the lower metal line made of a copper layer and the upper metal line made of an aluminum layer. Generally, a Ti or TiN layer, which is deposited through sputtering, is used as the diffusion barrier.
Further, the diffusion barrier must have a sufficient thickness to stably perform its function. However, while it is possible to prevent the production of a high resistance compound when the diffusion barrier has a sufficient thickness, as the thickness of the diffusion barrier is increased, the proportional thickness of the aluminum layer decreases, and in this case contact resistance cannot be decreased sufficiently.
Conversely, to improve the decrease in the contact resistance problem, the thickness of the diffusion barrier may be reduced. However, due to the diffusion of aluminum, of which the upper metal line is formed, voids can be formed in the aluminum layer and a high resistance compound is likely produced when the diffusion barrier thickness is reduced. As a result, the contact resistance is increased and both the semiconductor device characteristics and reliability will deteriorate.